Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity. In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
Deflectable catheters have been designed to provide deflection in at least one direction by a puller wire, if not also deflection in an opposite direction by a second puller wire. In such a construction, the puller wires extend into opposing off-axis lumens within a distal section of the catheter. For example, U.S. Pat. No. 6,210,407, the disclosure of which is incorporated herein by reference, is directed to a bi-directional catheter comprising two puller wires and a control handle having at least two moveable members longitudinally movable between first and second positions. The proximal end of each puller wire is connected to an associated movable member of the control handle. Proximal movement of a movable member relative to the catheter body results in proximal movement of the puller wire associated with that movable member relative to the catheter body, and thus deflection of the tip section in the direction of the lumen in which that puller wire extends.
While the aforementioned catheter provides bi-directional steering, the mechanical efficiencies of the steering and the deflection mechanism of the control handle can be improved upon. For example, the use of pulleys in the control handle can increase the throw capacity of the catheter. However, the repeated bending and straightening of the puller wires trained around the pulleys during deflection operations can significantly reduce the life span of the puller wires due to fatigue failure. If a different tensile material is trained around the pulleys, means for connecting this different material to a puller wire can pose additional challenges.
Current means for attaching puller wire ends typically involve mechanical crimping utilizing a stainless steel ferrule crimped on the puller wire end. The stainless to stainless steel crimping process may cause puller wire surface deformation (nicks or notches) that change the wire section modulus thus creating localized stress raisers that have a propensity to initiate crack propagation during puller wire tensile force cycling that occurs during catheter handle actuation. Due to limited space in the catheter shaft, the puller wire is designed to be as small as possible thus it is subjected to high tensile stresses during catheter handle operation. Any changes in the puller wire's cross sectional area in tension could result in puller wire failure during catheter operation. Hence, there is a desire for a deflectable catheter whose puller wire connections avoid such surface deformations.